An exemplary embodiment relates to the digital imaging arts. It finds particular application in conjunction with a method and apparatus for incorporating watermarks comprising small marks in blank portions of pages of documents. The watermarks may be used for embedding information in hard copy document borders or periphery which may be used to distinguish authentic hardcopy documents from counterfeit documents or for other applications.
Since print systems have been in existence, printers have sought methods for inhibiting counterfeiting and unauthorized copying of printed documents. Machine readable information in the form of watermarks, barcodes, and the like have been embedded into images on paper for a variety of applications, including document identification and authenticity verification. The code is generally invisible or visually unobtrusive and may be decoded by a device which is capable of reading the information. Current counterfeit prevention systems are frequently based on the use of digital watermarks. Digital watermarking is a technique which allows a user to add information (e.g., copyright notices, security codes, identification data, etc.) to digital image signals and documents. Such data can be in a group of bits describing information pertaining to the signal or to the author of the signal (e.g., name, place, etc.). Most common watermarking methods for images work in spatial or frequency domains. However, such techniques, while suitable for digital documents, are often not sufficiently robust to allow detection of the marks in hardcopies, i.e., when the digital document is rendered in physical form.
Additionally, many existing techniques are designed for a particular type of images, for example continuous-tone pictures or text. It is often difficult to select one algorithm for embedding a watermark on a page to be printed if the image type of the page is unknown. Another challenge for the existing technology is simplicity. Many methods require very complex calculations, either in embedding or in detection, and quite often, in both. Yet another challenge is to provide an embedding method which can be applied to both color images and black and white images. Some existing methods rely on embedding information in the yellow separation. They cannot be used for black and white printing devices.
U.S. Pat. No. 6,694,042, entitled METHODS FOR DETERMINING CONTENTS OF MEDIA, by Seder et al., discloses printing documents and other objects with machine readable indicia, such as steganographic digital watermarks or barcodes, for enabling document management functions. The indicia can be added as part of the printing process, such as by printer driver software, by a Postscript engine in a printer. The indicia can encode data about the document, or can encode an identifier that references a database record containing such data. By showing the printed document to a computer device with a suitable optical input device (e.g., a webcam), an electronic version of the document can be recalled for editing, or other responsive action can be taken.
Published Application No. 20060165255, entitled EMBEDDING VARIABLE WATERMARK INFORMATION IN HALFTONE SCREENS, by Wang et al., discloses incorporating correlated stochastic screens, time stamps, text messages, logos and other variable data into printed halftone images in real-time as invisible watermarks.
Published Application No. 20060061088, entitled METHOD AND APPARATUS FOR INTERNET COUPON FRAUD DETERRENCE, by Harrington et al., discloses embedding anti-counterfeiting marks that carry user information and other data into an original coupon design. The marks may be invisible, or visible but difficult to remove. At the receiving side of the coupons, the embedded data are used to detect fraud and trace back the coupon users.
Above-mentioned U.S. application Ser. No. 11/317,768 discloses a system which applies a security mark to a recipient, such as an image or document. A data reception component receives information from one or more sources. A security mark generation component generates at least one miniature security mark (MSM) configuration based at least in part upon the information from the data reception component. An application component applies the at least one MSM configuration to one or more recipients.
All disclosure provided in the above cited references is hereby incorporated by reference in their entirety herein for their teaching.
There remains a need for alternative systems and methods to provide non-invasive watermarking techniques which may be used for identification of images and/or documents, for uses such as prevention of counterfeiting, and for other purposes.
Thus in accordance with one aspect of an exemplary embodiment, a method for embedding information in a document includes receiving a digital image data document page, and checking the border of that page at the edge to determine if the border is blank. If the border is determined as not blank it is cleared of data. After receiving information to be embedded, it is encoded as a plurality of data carrying dot pair patterns. The dot pair patterns comprise dots too small to be visually noticeable when rendered. The encoded plurality of data carrying dot pair patterns are embedded in the border area of the document digital image area. The document with the embedded data carrying dot patterns is rendered.
In another aspect, a system for embedding information in a document includes a data reception component that receives information. A watermark embedding component in communication with the reception component embeds a watermark in a document to be rendered based at least in part upon the received information. The watermark embedding component identifies a sequence of blank blocks in the cleared border of a document page to be rendered and embeds the information as a plurality of data carrying dot patterns, each of the dot patterns being embedded in a respective blank block. The system further comprises a rendering unit or printer for rendering the embedded document where each of data carrying dot patterns in the border is rendered with each dot too small to be visually noticeable.
In another aspect, a recipient includes an image and a machine readable watermark embedded therein, the watermark comprising a plurality of data carrying dot patterns which each encodes data, each dot pattern comprising an arrangement of miniature marks which are substantially unnoticeable to an unaided eye, the dot patterns being each assigned to a respective one of a sequence of equally sized blank blocks arranged along the border of the recipient which been previously cleared of any image data thereupon assigned, whereby by examination of blank blocks containing no more than a threshold amount of image data, the dot patterns which are otherwise indiscernible, are retrievable and the data encoded therein interpreted.
In another aspect, a method for retrieving information embedded in blank border space in a rendered document includes inputting image data acquired from the rendered document, partitioning at least a portion of a document page represented by the image data into a plurality of equally sized blocks arranged along the edge as a border, and identifying, from among the blocks, a sequence of blank blocks which contain no more than a threshold amount of image data. For each block in the sequence of blank blocks, the method includes determining whether the block includes a pattern of miniature marks which corresponds to a unique datum value stored in a data structure. The information embedded is retrieved from the unique data values.
In another aspect, a system for retrieving information embedded in a document includes a detection component for generating a signal representative of image data acquired from a document, a data structure which links each of a plurality of predefined dot patterns with a unique datum value, and an extraction component for extracting a watermark from the image data, where present. The watermark includes a plurality of the dot patterns. The extraction component is configured for partitioning at least a portion of a document page border represented by the image data into a plurality of equally sized blocks, identifying, from among the blocks, a sequence of blank blocks which contain no more than a threshold amount of image data, for each of the sequence of blank blocks, determining whether the block includes a dot pattern otherwise too small to be visually noticeable and which corresponds to a unique datum value stored in the data structure. From the unique data values, the information embedded is retrieved. The system optionally includes an implementation component for implementing a computer implemented process in accordance with the retrieved information.